Gemstone
Complementary: Pure metals and metal alloys
Gemstones are only expensive because we cannot efficiently produce them in large quantities (yet) Gemstones are not expensive due to the scarcity of the chemical elements (like the case with gold and noble metals)
Bulk macroscale gemstones are hard but brittle.
They are not tough i.e. not capable of adsorbing a lot of energy on deformation
This can be subverted though by nano-structuring them.
See: Mechanical metamaterial, Emulated elasticity, Superelasticity.
Atommically precise gemstone nano-crystals (crystolecules) can be bent to all the way into the 2 digit percent range before breaking.
When smartly interwoven (think chainmaille but more advanced) some of these properties can be carried over to the macroscale again. Possibly adding novel formerly unachievable material properties.
For why pure metals and alloys are not a good base material for gem based APM see page:
Pure metals and metal alloys
"gemstone" vs "ceramics"
The term "gemstone" tends to immediately raises the association with high scarcity. But its still better than the term "diamond" that tends to instantly break suspense of disbelief dragging conversation into joke territory quenching any further serious discussion. Still the term "gemstone" tends to derail explanation attempts from things that are important upfront to things that should better be explained later.
- One first wants to explain why these kinds of materials are of highest interest (stiffness, difficulty test case in terms of mechanosynthesis)
- Only then one wants to explain why gemstones actually can become extremely abundant. And that they actually can (via the "easiness" of metamaterials) end civilizations dependence on resource that are much more fundamentally scarce (like e.g. alloying metals obsolete). Much more fundamentally scarce because they are chemical elements that fundamentally cannot be changed by chemical means.
The term "ceramics" may deliver a less wrong picture (no extreme scarcity -- and macroscale impact resilience through nano-crystallinity) but it it does so for the wrong reasons. Nano-crystals of ceramics are never atomically precise since they are always (pretty much by definition) created via statistical thermodynamic processes (high heat and pressure or even in case of natural biomineralisation there is statistical diffusion). Ceramics are dumb passive materials statistical in the small scales and homogeneous on larger scales. They are very different from gemstone based metamaterials which are neither statistical on the smaller scales nor homogeneous at the large scales.
Related
- Ceramics
- Diamond & Lonsdaleite = hexagonal diamond
- Moissanites – diamond-silicon-crossover (both compositional & structural variety)
- In contrast: Pure metals and metal alloys
Some especially interesting gemstones
- Dialondeites – diamond-lonsdaleite-structural-crossover
- Mechadensites – rutile-stishovite-compositional-crossover
- Stishovite & Seifertite – ultrahard quartz polymorphs
- Tistarite – rutile polymorph (featuring lekosapphire structure)
- Deltalumite – leukosapphire polymorph (? structure)
Compositional crossover means: Pseudo phase diagram
